The 32-year-old has penned a one-year deal at Stamford Bridge to become Jose Mourinho's sixth summer signing, with the club losing faith in its pursuit of Wayne Rooney
The 32-year-old previously played under Jose Mourinho at Inter, with a record of 53 goals in 102 appearances between 2009-11, and becomes the Portuguese's sixth summer signing.
Chelsea has tracked Manchester United striker Wayne Rooney for much of the summer, with two bids rejected, and Mourinho hinted last week that a third offer is coming before the end of the transfer window.
"It wasn't a hard decision. I saw the qualities Chelsea have, and I was very happy with Jose Mourinho before, so when the opportunity came, I was very happy to take it," Eto'o told the club's official website.
Eto'o becomes Chelsea's second summer recruit from the Russia outfit after Willian's arrival on Wednesday for 31.7 million pounds. The duo joins Cristian Cuevas, Andre Schurrle, Mark Schwarzer and Marco van Ginkel as summer arrivals at Stamford Bridge.